• Animal tissues and organs must be synced
  • hunting predator: nose → brain → muscles

• Animals have 2 systems for stimulus response

1. Endocrine: chemical signals released in bloodstream
2. Nervous: neurons transmit signals throughout body

• Endocrine signalling via hormones
  • many hormones with unique receptors

• Nervous system signalling via electrical pathways
  • nerve impulses travel to targeted destination

• The external environment is highly variable
  • fluctuates daily, seasonally, annually
  • especially on land

• Animals must maintain internal stability

• Regulators:

• Conformers:

• Animals may use both mechanisms
  • depends on the variable

• Animals exhibit homeostasis for many properties
  • temperature, pH, blood glucose, etc.

• Fluctuation in properties is a stimulus

• Animal detect stimulus by a receptor, which triggers a response
  • returns variable to target value

• Regulation occurs @ different life stages
  • hormones at puberty
  • larva vs adults

• Regulated changes can be cyclical
  • i.e. hormones and menstruation

• Circadian Rhythms =

• Why do humans get jet lag?

• Animals often move into different environments
  • changes in elevation, temperature, salinity, etc.
  • or seasons (without moving)

• May need to adjust homeostasis to new conditions
  • not permanent (or would be ‘adaptation’)

• Example: mammals reach high altitude
  • lower O₂ causes animals to breath rapid and deeply
  • more CO₂ is lost when exhaling, changing blood pH
  • over days, kidneys alter urine output to fix blood pH

• Thermoregulation:
  • impacts enzyme activity, cellular fluids, biochemistry

• Heat for thermoregulation can come from 2 sources

1. Internal metabolism: Endothermic
2. External sources: Ectothermic

• Endotherms can maintain temperatures in fluctuating environments
  • ability to heat or cool themselves

• Ectotherms adjust temperature via behaviors
  • seeking shade or sun

• Endotherms bodies are constantly losing heat
  • thermogenesis matches rates of heat loss

• Thermogenesis increased by muscle activity
  • moving
  • shivering

• Shivering common in birds and flying insects
  • ‘warming up’ flight muscles

• Insulation reduces flow of heat
  • fur, feathers, fat, oils
  • important for mammals and birds

• Insulation may be altered
  • raising hair or feathers when cold
  • goose bumps in humans!!!

• Insulation vital for marine mammals
  • water colder than body core
  • heat transfer faster in water than air

• Animals can alter blood flow when temperatures change
  • between internal body and skin

• Blood vessels can relax, making them wider
  • increases blood flow near skin to release heat

• Blood vessels can also constrict
  • reduces blood flow and prevents heat loss

Birds, mammals, sharks, insects often transfer heat between fluids moving in opposite directions

Arteries and veins located near each other

Heat transferred from warm blood (artery) to cold blood (vein) returning from extremities

• Group mechanisms to heat or cool
  • Huddling for warmth
  • Fanning to cool

• Emperor Penguins
  • dark plumage facing out
  • overlapping feathers
  • shivering
  • fat insulation
  • feet tipped up

• Social thermoregulation common in bees